Vatican spokesman Father Federico Lombardi reads from Pope Benedfict XVI's book "Light of the World" as he meets journalists at the Vatican, Monday, Feb. 11, 2013. Pope Benedict XVI announced Monday that he would resign Feb. 28 � the first pontiff to do so in nearly 600 years. The decision sets the stage for a conclave to elect a new pope before the end of March. (AP Photo/Gregorio Borgia)

Gallery: A look back at Pope Benedict XVI

The 85-year-old pope announced his decision in Latin during a meeting of Vatican cardinals.

“After having repeatedly examined my conscience before God, I have come to the certainty that my strengths due to an advanced age are no longer suited to an adequate exercise of the Petrine ministry,” he told the cardinals.

Benedict, the first pontiff to resign in nearly 600 years, emphasized that carrying out the duties of being pope — the leader of more than a billion Roman Catholics worldwide — requires “both strength of mind and body.” He says he is simply too infirm to carry on.